How do I create a widget for my armature
This could be one way to create a custom shape to control your bones: create a custom bone. https://youtu.be/6aRdurh30f0?t=1m9s

However, I'm sure you're more interested in this way, creating a custom shape that can control an aspect of a bone (like how the arrows in your image control the rotation of the door). https://youtu.be/8-IkdjzyJMQ?t=23m4s

Hope this helps!